DESCRIPTION: The investigators have identified three specific aims to address the hypothesis that IGF-IIR is involved in palatal growth and consequently in palatal closure. These aims are: 1) to determine the relationship between haplotype-specific rates of palatal development and IGF-IIR mRNA and protein expression; 2) to demonstrate a maternal effect on IGF-IIR mRNA and protein expression using matroclinus reciprocal crosses, and 3) to determine if the normal intrauterine environment is of greater or lesser influence than the similarity or dissimilarity of IGF-IIR genotype with respect to developmental variation. The first aim will be examined by quantitatively and qualitatively determining IGF-IIR mRNA and protein levels in palatal shelves from congenic strains of mice over four gestational days. These levels will be examined with palatal cell proliferation data to determine if there is a correlation between these endpoints. The second aim will be a repeat of the experiments under the first aim; however, the animals to be used for these experiments will be the (F1) hybrid mice from reciprocal crosses of the congenic mouse strains. In this manner the investigators can determine if the factor segregates with the maternal genotype as IGF-IIR is known to do. The final aim will be examined by a statistical analysis of PCNA results in offspring from homozygous B10.A mice vs offspring from mice heterozygous for the congenic portion of chromosome 17 in which four genotypes should be present.